Selling, General and Administrative Expense
Selling, general and administrative expense for the three months ended September 30, 2021 of $3.6 million increased by $1.3 million, or 58%, when compared to the three months ended September 30, 2020. The increase is due to a $0.4 million increase in compensation costs related to growth in headcount along with a $0.9 million increase in other costs of growing the business. We expect selling, general and administrative costs to increase to support our growth and as a result of the administrative costs of the expected merger and increased costs for infrastructure required as a public company.
Interest Expense
Interest expenses for the three months ended September 30, 2021 of $75 thousand increased by 19%, when compared to the three months ended September 30, 2020, primarily due to higher outstanding debt.
Income Tax Expense
Income tax expenses for the three months ended September 30, 2021 increased by $13 thousand when compared to the three months ended September 30, 2020. We expect our tax rate to remain close to zero in the near term due to full valuation allowances against deferred tax assets.
Comparison of the Nine Months ended September 30, 2021 and 2020
Revenue
Revenue for the nine months ended September 30, 2021 was $16.4 million compared to $7.2 million for the nine months ended September 30, 2020, an increase of $9.2 million, or 128%. The increase reflected the achievement of expansion of product and end-customer base and total sales volumes increasing 187%, from 6.1 million to 17.5 million GaN ICs shipped.
Cost of Goods Sold
Cost of goods sold for the nine months ended September 30, 2021 was $9.0 million, an increase of $3.9 million or 78% compared to the nine months ended September 30, 2020. The increase was primarily driven by significant revenue growth, partially offset by lower costs on second generation (“Gen 2”) products launched in the second half of 2020 combined with third generation (“Gen 3”) products launched in 2021 that represented the majority of cost of goods sold. Gen 2 provides consistent manufacturing yields in excess of 90%, while Gen 3 improved energy savings by up to an additional 10% compared to prior generations, as well as further reduced external component count and shrank system footprints .
Research and Development Expense
Research and development expense for the nine months ended September 30, 2021 of $16.3 million increased by $8.2 million, or 101%, when compared to the nine months ended September 30, 2020, primarily driven by increases in headcount and stock based compensation resulting in $4.3 million and $1.7 million higher compensation costs, respectively, along with an increase of $2.2 million in non-compensation costs related to new applications and reliability expenses devoted to next generation product development. We expect research and development expense to continue to increase as we grow our headcount to support our expansion into new applications.
Selling, General and Administrative Expense
Selling, general and administrative expense for the nine months ended September 30, 2021 of $23.7 million increased by $18.1 million, or 322%, when compared to the nine months ended September 30, 2020. The increase is primarily due to a $12.8 million increase in stock-based compensation, of which $12.6 million was related to rescinded restricted stock grants, a $2.2 million increase in compensation costs related to growth in headcount and a $3.1 million increase in other costs of growing the business. We expect selling, general and administrative costs to increase to support our growth and as a result of the administrative costs of the expected merger and increased costs for infrastructure required as a public company.