the fiscal 2021 period compared to the prior fiscal year period. Direct and indirect sales to Nokia, currently our largest customer, decreased from $6.0 million in the three months ended June 30, 2019 to $1.8 million in the three months ended June 30, 2020. Shipments of our SigmaQuad product line accounted for 46.3% of total shipments in the three months ended June 30, 2020 compared to 67.9% of total shipments in the three months ended June 30, 2019. The changes in SigmaQuad shipments were primarily due to the changes in sales to Nokia discussed above.
Cost of Revenues. Cost of revenues decreased by 25.2% from $4.8 million in the three months ended June 30, 2019 to $3.6 million in the three months ended June 30, 2020. Cost of revenues included a provision for excess and obsolete inventories of $159,000 in the three months ended June 30, 2020 compared to $89,000 in the three months ended June 30, 2019. Cost of revenues included stock-based compensation expense of $55,000 and $88,000 for the three months ended June 30, 2019 and 2020, respectively.
Gross Profit. Gross profit decreased by 63.0% from $8.2 million in the three months ended June 30, 2019 to $3.1 million in the three months ended June 30, 2020.
Gross margin decreased from 63.3% in the three months ended June 30, 2019 to 46.1% in the three months ended June 30, 2020. The change in gross profit was primarily related to the changes in net revenues discussed above. The change in gross margin was primarily related to changes in the mix of products and customers and changes in the level of charges for inventory reserves booked in each period.
Research and Development Expenses. Research and development expenses increased by 4.1% from $5.6 million in the three months ended June 30, 2019 to $5.8 million in the three months ended June 30, 2020. The increase in research and development spending was primarily related to an increase of $109,000 for payroll related expenses, and lesser increases in software maintenance expenses, rent expense and professional fees. Research and development expenses included stock-based compensation expense of $399,000 and $413,000 for the three months ended June 30, 2019 and 2020, respectively. The increases in research and development spending was primarily related to the development of our associative computing devices.
Selling, General and Administrative Expenses. Selling, general and administrative expenses were unchanged at $2.9 million in the three months ended June 30, 2019 and in the three months ended June 30, 2020. A decrease of $200,000 for independent sales representatives commissions and a lesser decrease in travel related expenses was primarily offset by an increase in professional fees and payroll related expenses. Selling, general and administrative expenses included stock-based compensation expense of $197,000 and $254,000 for the three months ended June 30, 2019 and 2020, respectively.
Interest Income, Net. Interest and other income, net decreased 27.9% from income of $147,000 in the three months ended June 30, 2019 to $106,000 in the three months ended June 30, 2020. Interest income decreased by $91,000 due to lower interest rates received on our cash and short-term and long-term investments. Foreign exchange losses were $58,000 for the three months ended June 30, 2019 compared to $8,000 for the three months ended June 30, 2020. The exchange losses are related to our Taiwan branch operations and our operations in Israel.
Provision for Income Taxes. The provision for income taxes increased 1,032.6% from $43,000 in the three months ended June 30, 2019 to $487,000 in the three months ended June 30, 2020. This change was primarily due to the settlement of an income tax audit in Israel during the quarter ended June 30, 2020 for fiscal years 2016 through fiscal 2019 which resulted in a discrete tax provision of $479,000, and to a lesser extent due to fluctuations in the relative mix of income among our operating jurisdictions.
Net Income (Loss). Net loss was $125,000 in the three months ended June 30, 2019 compared to $6.1 million in the three months ended June 30, 2020. This fluctuation was primarily due to the changes in net revenues, gross profit and operating expenses discussed above.
Liquidity and Capital Resources
As of June 30, 2020, our principal sources of liquidity were cash, cash equivalents and short-term investments of $64.6 million compared to $66.6 million as of March 31, 2020.