Bernie Blegen
Vice President & Chief Financial Officer at Monolithic Power Systems
Thanks, Gen.
MPS achieved record second quarter revenue of $461.0 million, 22.1% higher than the first quarter of 2022, and 57.2% higher than the second quarter of 2021. This broad-based year-over-year revenue growth was a result of consistent execution against our strategies.
Turning now to the second quarter 2022 revenue by market. In our enterprise data market, second quarter 2022 revenue of $65.2 million increased 53.4% from the first quarter of 2022, primarily due to an accelerated ramp in our data center and workstation computing sales. Second quarter 2022 revenue was up 117.9% year-over-year. Enterprise data revenue represented 14.2% of MPS's second quarter 2022 revenue compared with 10.2% in the second quarter of 2021. Storage and computing revenue of $122.3 million increased 26.6% from the first quarter of 2022. The sequential revenue improvement reflected higher commercial notebook and storage sales.
Second quarter 2022 revenue was up 111.6% year-over-year. Storage and computing revenue represented 26.5% of MPS's second quarter 2022 revenue compared with 19.7% in the second quarter of 2021. Second quarter consumer market revenue of $97.3 million increased 21.7% from the first quarter of 2022. The sequential quarterly revenue improvement was broad-based with particular strength noted in home appliances and gaming. Second quarter 2022 revenue was up 27.9% year-over-year. Consumer revenue represented 21.1% of MPS's second quarter 2022 revenue compared with 25.9% in the second quarter of 2021.
Second quarter 2022 industrial revenue of $55.9 million increased 15.1% from the first quarter of 2022, reflecting increased sales of products for power source and security applications. Second quarter 2022 revenue was up 28.9% year-over-year. Industrial revenue represented 12.1% of our total second quarter 2022 revenue compared with 14.8% in the second quarter of 2021. Second quarter automobile revenue of $61.0 million increased 11.9% from the first quarter of 2022. Primarily -- due primarily to increased sales of applications for advanced driver system systems, the digital cockpit and lighting products.
Second quarter 2022 revenue was up 25.3% year-over-year. Automotive revenue represented 13.2% of MPS's second quarter 2022 revenue compared with 16.6% in the second quarter of 2021. Second quarter 2022 communications revenue of $59.3 million was up 6.7% from the first quarter of 2022. Most of the sequential revenue increase was related to 5G infrastructure. Second quarter 2022 revenue was up 58.3% year-over-year. Communications sales represented 12.9% of our total second quarter 2022 revenue compared with 12.8% in the second quarter of 2021.
Moving now to a few comments on gross margin. GAAP gross margin was 58.8%, 90 basis points higher than the first quarter of 2022 and 280 basis points higher than the second quarter of 2021. Our GAAP operating income was $141.9 million compared to $96.1 million reported in the first quarter of 2022 and $60.6 million reported in the second quarter of 2021.
Non-GAAP gross margin for the second quarter of 2022 was 59.0%, up 70 basis points from the gross margin reported for the first quarter of 2022 and 270 basis points higher than the second quarter from a year ago. The quarter-over-quarter and year-over-year increases in both GAAP and non-GAAP gross margin is attributed largely to operational efficiency gains and a more favorable sales mix. Our non-GAAP operating income was $179.4 million compared to $133.6 million reported in the first quarter of 2022.
Let's review our operating expenses. Our GAAP operating expenses were $129.1 million in the second quarter of 2022 compared with $122.7 million in the first quarter of 2022 and $103.6 million in the second quarter of 2021. Our non-GAAP second quarter 2022 operating expenses were $92.7 million, up from the $86.6 million we spent in the first quarter of 2022 and up from the $70.3 million reported in the second quarter of 2021. The differences between non-GAAP operating expenses and GAAP operating expenses for the quarters discussed here are primarily stock compensation expense and income or loss on an unfunded deferred compensation plan.
For the second quarter of 2022, total stock compensation expense, including approximately $1.2 million charged to cost of goods sold was $42.9 million compared with $39.8 million recorded in the first quarter of 2022. Our second quarter 2022 GAAP other income -- other expense was $5.1 million compared with $634,000 in the first quarter of 2022.
Our second quarter 2022 non-GAAP other expense was $7,000 compared with non-GAAP other income of $1.6 million in the first quarter of 2022. The decrease is due to a $2 million increase in charitable contributions, partly offset by the favorable impact of currency exchange rates. The difference in non-GAAP other income and GAAP other income is the income or loss on an unfunded deferred compensation plan.
Switching to the bottom line. Second quarter 2022 GAAP net income was $114.7 million or $2.37 per fully diluted share compared with $79.6 million or $1.65 per share in the first quarter of 2022 and $55.2 million or $1.16 per share in the second quarter of 2021. Second quarter 2022 non-GAAP net income was $157.0 million, or $3.25 per fully diluted share compared with $118.3 million or $2.45 per fully diluted share in the first quarter of 2022 and $86.5 million or $1.81 on a per share -- per fully diluted share in the second quarter of 2021. Fully diluted shares outstanding at the end of Q2 2022 were 48.3 million.
Now let's look at the balance sheet. Cash, cash equivalents and investments were $814.1 million at the end of the second quarter of 2022 compared with $775.9 million at the end of the first quarter of 2022. For the quarter, MPS generated operating cash flow of approximately $105.2 million compared with Q1 2022 operating cash flow of $107.4 million. Accounts receivable ended the second quarter of 2022 at $125.5 million, representing 25 days of sales outstanding, which was 4 days lower than the 29 days reported at the end of the first quarter of 2022 and 1 day higher than the 24 days in the second quarter of 2021.
Our internal inventories at the end of the second quarter of 2022 were $359.6 million, up from the $311 million at the end of the first quarter of 2022. Days of inventory of 172 days at the end of the second quarter of 2022 were 6 days lower than at the end of the first quarter of 2022. Historically, we have calculated days of inventory on hand as a function of current order revenue. We believe comparing current inventory levels with the following quarter's revenue provides a better economic match. On this basis, you can see days of inventory of 162 days at the end of the second quarter of 2022, which were 13 days higher than the 149 days at the end of the first quarter of 2022 and 44 days higher than the 118 days at the end of the second quarter of 2021.
I would like now to turn to our outlook for the third quarter of 2022. We are forecasting Q3 revenue in the range of $480 million to $500 million; GAAP gross margin in the range of 58.4% to 59.0%; non-GAAP gross margin in the range of 58.7% to 59.3%; total stock-based compensation expense in the range of $42.8 million to $44.8 million, including approximately $1.3 million that would be charged to cost of goods sold; GAAP R&D and SG&A expenses between $136.2 million and $140.2 million; non-GAAP R&D and SG&A expenses in the range of $94.7 million to $96.7 million; litigation expense in the range between $2.3 million and $2.7 million; interest and other income in the range from $1.3 million to $1.7 million before foreign exchange gains and losses; fully diluted shares in the range of 47.9 million to 48.9 million shares.
In conclusion, we are continuing to execute on our growth strategies, including expansion and diversification of our R&D centers and manufacturing partnerships in multiple countries.
I will now open the webinar up for questions.