Gross profit may vary from quarter-to-quarter and is primarily affected by our ASP, product costs, product mix, customer mix, geographical mix, shipping method, warranty costs and seasonality.
Operating Expenses
Operating expenses consist of research and development expenses, selling and marketing expenses and general and administrative expenses. Personnel-related costs are the most significant component of our operating expenses and include salaries, benefits, bonuses, commissions and stock-based compensation expenses.
Our full-time employee headcount in research and development, sales and marketing and general and administrative capacities has grown from 25, three and eight as of December 31, 2019 to 43, 13 and 32 as of December 31, 2020, respectively, and we expect to continue to hire new employees to support our growth.
The timing of these additional hires could materially affect our operating expenses in any particular period, both in absolute dollars and as a percentage of revenue. We expect to continue to invest substantial resources to support our growth and anticipate that each of the following categories of operating expenses will increase in absolute dollar amounts for the foreseeable future.
Research and Development Expenses
Research and development expenses consist primarily of salaries, employee benefits, stock-based compensation expenses and travel expenses related to our engineers performing research and development activities to originate, develop and enhance our products. Additional expenses include consulting charges, component purchases, legal fees for registering patents and other costs for performing research and development on our software products.
Selling and Marketing Expenses
Selling and marketing expenses consist primarily of salaries, employee benefits, stock-based compensation expenses and travel expenses related to our sales and marketing and business development personnel. Additionally, selling and marketing expenses include costs associated with professional fees and support charges for software subscriptions and licenses, trade shows and conventions.
We expect an increase in the number of sales and marketing personnel in connection with the expansion of our global sales and marketing footprint as we enter new markets. The majority of our sales and marketing expenses in 2019 and 2020 were related to customers in the United States and business development in other parts of the world. As of December 31, 2020, we have a sales presence in the United States, Asia , the Middle East, North Africa and Australia. We intend to continue to expand our sales presence and marketing efforts to additional countries.
General and Administrative Expenses
General and administrative expenses consist primarily of salaries, employee benefits, stock-based compensation expenses, and travel expenses related to our executives, finance team, and the administrative employees. It also consists of legal, consulting, and professional fees, rent and lease expenses pertaining to our international offices, business insurance costs and other costs. We also expect that after completion of this offering, we will incur additional audit, tax, accounting, legal and other costs related to compliance with applicable securities and other regulations, as well as additional insurance, investor relations and other costs associated with being a public company.
Non-Operating Expenses and Other Items
Interest Expense
Interest expense consists of interest payments, annual amortization of debt issuance costs and loss on debt extinguishment in connection with our Secured Promissory Notes which we sold through a private placement and which we had repaid the principal in full as of December 31, 2020, and a revolving line of credit with Western Alliance Bank, which matures on June 10, 2021 (See “Debt Obligations” below).
Benefit from Income Taxes
Benefit from income taxes consists primarily of income taxes related to foreign and state jurisdictions in which we conduct business.