In this paper we have developed a passivation technique with silicon-nitride (SiNX) film that requires no surface pre-treatment, and is fully compatible to monolithic microwave integrated circuits (MMICs). The nitride depositions were carried out by ECR-CVD (electron cyclotron resonance-chemical vapor deposition) directly over InGaP/GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Optical emission spectrometry (OES) was used for plasma characterization, and low formation of H and NH molecules in the gas phase was detected at pressure of 2.5 mTorr. These molecules can degrade III-V semiconductor surfaces due to the preferential loss of As or P and hydrogen incorporation at the substrate. The substrates were cleaned with organic solvents using a Sox-let distillate. The ECR depositions were carried out at a fixed substrate temperature of 20 °C, SiH4/N2 flow ratio of 1, Ar flow of 5 sccm pressure of 2.5 mTorr and microwave (2.45 GHz) power of 250 W and RF (13.56 MHz) power of 4 W. We have applied this film for InGaP/GaAs HBT fabrication process with excellent results, where two major contribuiton is related to this passivation technique, the enhancement in the transistor dc gain β and the improvement in the signal-to-noise ratio when compared unpassivated and passivated devices. © 2008.2541960636066Li, X., Cao, Y., Hall, D.C., Fay, P., Han, B., Wibowo, A., Pan, N., (2004) IEEE Electron Devices Lett., 25, p. 773Jin, Z., Neumann, S., Prost, W., Tegude, F., (2005) Solid-State Electron., 49 (3), p. 409Jin, Z., Otten, F., Reimann, T., Neumann, S., Prost, W., Tegude, F., (2004) J. Solid-State Electron., 48 (9), p. 1637Yoshioka, R.T., de Barros Jr., L.E.M., Diniz, J.A., Swart, J.W., (1999) Proceedings of the International Microwave and Optoelectronics Conference, 1999. SBMO/IEEE MTT-S, APS and LEOS-IMOC '99, vol. 1, p. 108Zoccal, L.B., Diniz, J.A., Doi, I., Swart, J.W., Daltrini, A.M., Moshkalyov, S.A., (2006) J. Vac. Sci. Technol. B, 24, p. 1762Cheng, S.-Y., Fu, S.-I., Liu, W.-C., (2007) J. Vac. Sci. Technol. B, 25 (June 3), p. 734