A narrow linewidth semiconductor laser device has a semiconductor laser and a low noise current source operatively connected to the laser with the current source being adapted to prevent degradation of the laser's frequency noise spectrum. An optical frequency discriminator provides an error signal representative of the laser's optical frequency and a control circuit has a feedback network that provides a frequency feedback signal that is adapted to the frequency noise spectrum of the frequency discriminator and to the laser's frequency noise spectrum and tuning response. The control circuit also has a sequencer to automatically enable frequency locking of the laser on the frequency reference of the optical frequency discriminator. An enclosure encloses the frequency discriminator to isolate the frequency discriminator from external perturbations. The device provides an improved sub-kHz linewidth and a high coherence while being compact, lightweight and highly reliable, as well as being automatically operated.