Stock-Based Compensation

6 Months Ended

Jun. 30, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

4. Stock-Based Compensation

The Company uses the Black-Scholes option pricing model to calculate the fair value of stock option awards as of their grant date. Stock-based compensation expense for the three and six months ended June 30 was as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2015		2014		2015		2014

Cost of revenues	$	58	$	64	$	119	$	100
Selling, general and administrative		352		373		760		564
Research and development		78		100		172		107

Total stock-based compensation	$	488	$	537	$	1,051	$	771

The increase in selling, general and administrative stock-based compensation for the six months ended June 30, 2015 compared to the same period a year ago is primarily due to increased expense for certain Vicor stock options held by a non-employee. The fair value of these stock options, and related stock-based compensation, are adjusted monthly based on changes in the assumptions under the Black-Scholes option pricing model, including the price of the Company’s common stock, in accordance with the accounting for stock options granted to non-employees.

On December 31, 2010, the Company granted 2,984,250 non-qualified stock options under the VI Chip 2007 Stock Option and Incentive Plan with performance-based vesting provisions tied to achievement of certain margin targets by the VI Chip subsidiary. As of December 31, 2010, the Company determined it was probable the margin targets could be achieved and, accordingly, began recording stock-based compensation expense relating to these options beginning January 1, 2011. This determination remains the same as of June 30, 2015 and, accordingly, expense has been recorded through that date. The unrecognized compensation expense for these performance-based options was approximately $542,000 as of June 30, 2015.