Pursuant to the 1996 Plan, the exercise price for incentive stock options and non-statutory stock options is determined to be the fair market value of the underlying shares on the date of grant. Options typically vest ratably over a four-year period measured from the date of grant. Options generally expire no later than ten years after the date of grant, subject to earlier termination upon an optionee's cessation of employment or service.

RSUs granted to employees typically vest ratably over a four-year period and are converted into shares of the Company's common stock upon vesting, subject to the employee's continued service to the Company over that period.

MSUs granted to employees typically vest ratably over a two to four-year period and are converted into shares of the Company's common stock upon vesting, subject to the employee's continued service to the Company over that period. The number of shares that are released at the end of the performance period can range from zero to a maximum cap depending on the Company's performance. The performance metrics of this program are based on relative performance of the Company’s stock price as compared to the Semiconductor Exchange Traded Fund index XSD (the “SPDR S&P”).

The fair value of options granted to employees under the 1996 Plan is estimated on the date of grant using the Black-Scholes option valuation model.

Expected volatilities are based on the historical volatilities from the Company’s traded common stock over a period equal to the expected term. The Company is utilizing the simplified method to estimate expected holding periods. The risk-free interest rate is based on the U.S. Treasury yield. The Company determines the dividend yield by dividing the annualized dividends per share by the prior quarter’s average stock price. The Company also estimates forfeitures at the time of grant and makes revisions to forfeitures on a quarterly basis.

Restricted Stock Units and Other Awards

The fair value of RSUs and other awards under the Company’s 1996 Plan is estimated using the value of the Company’s common stock on the date of grant, reduced by the present value of dividends expected to be paid on the Company’s common stock prior to vesting. The Company also estimates forfeitures at the time of grant and makes revisions to forfeitures on a quarterly basis.

Market Stock Units

The Company granted MSUs to senior members of management in September 2015 and September 2016. The grant of MSUs was in lieu of granting stock options. MSUs are valued based on the relative performance of the Company’s stock price as compared to the Semiconductor Exchange Traded Fund index XSD (the “SPDR S&P”). The fair value of MSUs is estimated using a Monte Carlo simulation model on the date of grant. The Company also estimates forfeitures at the time of grant and makes revisions to forfeitures on a quarterly basis. Compensation expense is recognized based on the initial valuation and is not subsequently adjusted as a result of the Company’s performance relative to that of the XSD index. Vesting for MSUs is contingent upon both service and market conditions, and has a four-year vesting cliff period.

Employees are granted rights to acquire common stock under the 2008 ESPP.

The fair value of ESPP rights granted to employees has been estimated at the date of grant using the Black-Scholes option valuation model using the following assumptions for the offering periods outstanding: