T. Bernie Blegen
Vice President and Chief Financial Officer at Monolithic Power Systems
Thanks, Gen. MPS posted record first quarter revenue of $377.7 million, 48.4% higher than the first quarter of 2021. The year-over-year revenue increase represented strength in the overall market and, more importantly, broad-based market share gains resulting from customer acceptance of our new product introductions. Before looking at our revenue by market, I would like to call your attention to a change in our reporting. In order to provide increased visibility on data center and cloud computing revenue, we broke reporting for computer and storage into two separate line items. The table has been included in this webinar showing the company's quarterly revenue on this basis since 2017. The first line item is called storage and computing, which primarily refers to total storage and client computing revenue.
The second line item is called enterprise data, which captures revenue from data center and cloud computing. In our storage and computing market, first quarter 2022 revenue of $96.6 million increased $18.6 million or 23.9% from the fourth quarter of 2021 due primarily to higher storage and commercial notebook sales. Computing -- storage and computing revenue represented 25.6% of MPS' first quarter 2022 revenue compared with 20.2% in the first quarter of 2021. In our enterprise data market, first quarter 2022 revenue of $42.5 million increased 5.0% in the fourth quarter of 2021 due primarily to continuing strength in data center and workstation computing sales.
Enterprise data revenue represented 11.3% of MPS' first quarter 2022 revenue compared with 6.4% in the first quarter of 2021. First quarter 2022 communications revenue of $55.6 million rose $9.7 million or 21.1% from the fourth quarter of 2021. The quarter-over-quarter increase primarily reflected higher revenue related to 5G build-outs and satellite communications. Communications revenue represented 14.7% of MPS' first quarter 2022 revenue compared with 14.2% in the first quarter of 2021. First quarter 2022 revenue from consumer markets of $80.0 million increased $13.6 million or 20.6% from the fourth quarter of 2021. This sequential quarterly improvement -- this sequential revenue increase reflected a broad-based increase particularly related to our IoT business.
Consumer revenue represented 21.2% of our Q1 revenue compared with a 26.0% contribution in the first quarter of 2021. First quarter 2022 automotive revenue of $54.5 million decreased 3.2% from the fourth quarter of 2021. Automotive revenue represented 14.4% of MPS' first quarter 2022 revenue compared with 17.6% in the previous year. In our industrial market, revenue of $48.5 million was essentially flat with revenue recorded in the fourth quarter of 2021. Industrial revenue represented 12.8% of our first quarter revenue compared with 15.6% in the prior year. Moving now to a few comments on gross margin. GAAP gross margin was 57.9%, 30 basis points higher than the fourth quarter of 2021 and 250 basis points higher than the first quarter of 2021. Our GAAP operating income was $96.1 million compared with $78.6 million reported in the fourth quarter of 2021.
For the first quarter of 2022, non-GAAP gross margin was 58.3%, 40 basis points better than the fourth quarter of 2021 and 250 basis points better than the first quarter of 2021. Our non-GAAP operating income was $133.6 million compared to $112.0 million reported in the fourth quarter of 2021. On both a GAAP and a non-GAAP basis, the sequential quarterly gross margin improvement was primarily due to a better product mix as revenue from higher-value new product introductions are ramping. Let's review our operating expenses. Our GAAP operating expenses were $122.7 million in the first quarter of 2022 compared with $115.3 million in the fourth quarter of 2021. Our non-GAAP first quarter 2022 operating expenses were $86.6 million, up from $83.0 million reported in the fourth quarter of 2021.
The differences between non-GAAP operating expenses and GAAP operating expenses for the quarters discussed here are stock compensation expense, amortization of purchased intangibles and income or loss on an unfunded deferred compensation plan. For the first quarter of 2022, stock compensation expense, including approximately $1.3 million charged to cost of goods sold, was $39.8 million compared with $31.2 million recorded in the fourth quarter of 2021. Switching to the bottom line. First quarter 2022 GAAP net income was $79.6 million or $1.65 per fully diluted share compared with $72.7 million or $1.51 per share in the fourth quarter of 2021. First quarter 2022 non-GAAP net income was $118.3 million or $2.45 per fully diluted share compared with $102.1 million or $2.12 per fully diluted share in the fourth quarter of 2021. Fully diluted shares outstanding at the end of Q1 2022 were 48.2 million.
Let's look at the balance sheet. Cash, cash equivalents and investments were $775.9 million at the end of the first quarter of 2022 compared to $727.5 million at the end of the fourth quarter of 2021. For the quarter, MPS generated operating cash flow of about $107.4 million compared with operating cash flow of $28.2 million in the fourth quarter of 2021. First quarter 2022 capital spending totaled $26.5 million. Accounts receivable ended the first quarter of 2022 at $120.3 million or 29 days of sales outstanding, up one day from 28 days at the end of the fourth quarter of 2021. Our internal inventories at the end of the first quarter of 2020 were $311.0 million, up from the $259.4 million at the end of the fourth quarter of 2021. Days of inventory increased to 178 days at the end of Q1 2022 compared with 166 days at the end of the fourth quarter of 2021.
Historically, we've calculated days of inventory on hand as a function of the current quarter revenue. We believe comparing current inventory levels with the following quarter's projected revenue provides a better economic match. On this basis, again, as you can see, days of inventory increased to 159 days at the end of the first quarter of 2022, up from 149 days at the end of the fourth quarter of 2021. I would now like to turn to our outlook for the second quarter of 2022. We are forecasting Q2 revenue in the range of $420 million to $440 million. We also expect the following: GAAP gross margin in the range of 58.4% to 59.0%; n
On-GAAP gross margin in the range of 58.7% and 59.3%; GAAP R&D and SG&A expenses between $132.7 million and $136.7 million; non-GAAP R&D and SG&A expenses to be in the range of $90.0 million to $92.0 million, this estimate excludes stock compensation and litigation expenses; total stock-based compensation expense of $44.2 million to $46.2 million, including approximately $1.5 million that would be charged to cost of goods sold; litigation expenses ranging between $2.3 million and $2.7 million; interest and other income is expected to range from $1.3 million to $1.7 million before foreign exchange gains or losses; fully diluted shares to be in the range of 47.8 million to 48.8 million shares. In conclusion, we will continue to execute on our long-term plan for sustainable growth. I will now open the webinar up for questions.