In this paper we will describe applications of a low temperature SiNx for the novel fabrication of lasers and FET's. Sidewall roughness which appears on dry etched semiconductor laser mesas is a common problem in laser fabrication. Protecting the sidewall with a low temperature PECVD SiNx can greatly reduce laser mesa roughness that occurs during dry etching of the mesa. Another application uses low temperature SiNx to extend the resolution of standard optical replication. Submicron gate fingers in field effect transistors can be fabricated by using this low-temperature SiNx deposition. By depositing SiNx on the photoresist gate pattern and etching back the SiNx leaving a sidewall, this will reduce the opening of gate features. Submicron gate length MESFETs have been demonstrated with this technique which showed comparable results to conventional submicron MESFETs fabricated with E-beam direct writing.