We have developed plasma-deposited semi-inrulating rilicon nitride (SinSiN) as a reGstive sea passivation. In thir paper we briefly review itr properties, then we review how it can be used ar a resistive sea. Finally, we show that SinSiN can be used to improve the breakdown voltage of a high-voltage device by some 20 to 40 V by screening all surface charges. We further show that SinSiN provides device immunity to rurface charges, thereby improving yield and reliability.