Research and development costs were $22.4 million for the six months June 30, 2021, compared to $15.5 million for the six months ended June 30, 2020. The $6.9 million increase mainly reflected a $2.6 million increase in personnel-related costs and recruiting expenses for personnel in research and development departments, a $3.1 million increase in stock compensation expense, a $0.5 million increase in accounting and auditing expenses, and a $0.3 increase in software subscription licenses with the remainder due to changes in employee-related benefits, depreciation, and other research and development expenses.
Sales and Marketing
Sales and Marketing expenses were $1.1 million for the three months ended June 30, 2021. There were no sales and marketing expenses in the three months ended June 30, 2020 as the Company was primarily focused on research and development activities.
Sales and Marketing expenses were $1.2 million for the six months ended June 30, 2021. There were no sales and marketing expenses in the six months ended June 30, 2020 as the Company was primarily focused on research and development activities.
General and Administrative
General and administrative expenses were $18.3 million for the three months ended June 30, 2021, compared to $3.9 million for the three months ended June 30, 2020. The $14.4 million increase was primarily due to a $7.2 million increase in stock-based compensation expense, a $2.2 million increase from transaction costs incurred and expensed by the Company in relation to the Business Combination, a $1.5 million increase in third-party consulting and recruitment costs, a $1.5 million increase in employee-related costs, a $0.8 million increase in accounting and legal related expenses, with the remainder due to changes in facilities costs, legal fees and software subscription fees.
General and administrative expenses were $30.9 million for the six months ended June 30, 2021, compared to $7.0 million for the six months ended June 30, 2020. The $23.9 million increase was primarily due to a $14.1 million increase in stock-based compensation expense, a $2.2 million increase from transaction costs incurred and expensed by the Company in relation to the business combination, a $1.9 million increase in employee costs, a $2.7 million increase in third-party consulting and recruitment costs, $0.6 million increase in legal expense, a $1.2 million increase in accounting and audit fees, and a $0.8 million increase in facility and rent, with the remainder due to changes in facilities costs, IT equipment fees, and software subscription fees.
Interest Expense, Net
Interest expense, net was $0.7 million for the three months ended June 30, 2021, compared to $1.2 million for the three months ended June 30, 2020. The $0.5 million decrease in interest expense was primarily due to the settlement of convertible notes on January 28, 2021, therefore no interest expense related to convertible notes for three months ended June 30, 2021 while we incurred $1.1 million interest expense related to convertible notes for three months ended June 30, 2020, offset by an increase of $0.6 million in interest expense related to Bridge Loan and SVB loan for three months ended June 30, 2021.
Interest expense, net was $1.2 million for the six months ended June 30, 2021, compared to $2.2 million for the six months ended June 30, 2020. The $1.0 million decrease in interest expense was primarily due to the settlement of convertible notes on January 28, 2021, therefore we incurred $0.5 million and $2.2 million interest expense related to convertible notes for six months ended June 30, 2021 and 2020, respectively, offset by an increase of $0.6 million in interest expense related to Bridge Loan and SVB loan for six months ended June 30, 2021.
Other (Expense) Income, Net
Other expense, net was $0.7 million for the three months ended June 30, 2021, compared to $3.5 million other income, net for the three months ended June 30, 2020. The change was primarily due to a $2.5 million in income from a gain on the mark to market derivative liability related to convertible notes and a $1.0 million in income from government research and development contracts for the three months ended June 30, 2020. The remaining $0.8 million was due to a nonrecurring payment to one of our investors for three months ended June 30, 2021.
Other expense, net was $0.7 million for the six months ended June 30, 2021, compared to $4.0 million other income, net for the six months ended June 30, 2020. The change was primarily due to $2.8 million in income from a gain on the mark to market derivative liability related to convertible notes and a $1.0 million in income from government’s research and development contracts for the three months ended June 30, 2020. The remaining of $0.8 million was due to a nonrecurring payment to one of our investors for three months ended June 30, 2021.
Loss on Extinguishment of Convertible Notes
There was no such loss for the three months ended June 30, 2021 and 2020.
34