An etch-back polymide planarization process for the emitter contact of AlGaAs/GaAs HBTs using PC-1500 is presented. The degree of surface topography has a major impact on the yield in HBT fabrication. A planarization process using a spin-on sacrificial layer to produce a planar interlevel dielectric layer would be very beneficial in allowing thicker and more uniform emitter contacts therefore enhancing the yield and current handling capability. The PC-1500 polymer flows at 200°C and provides a much better planarity than regular photoresist. For patterns from -3 μm to 250 this polymer can achieve 80% to 92% planarity. The wafers were etched in a parallel plate, single wafer reactive ion-etching system with a mixture of oxygen and Freon-14. The etch rate of this polymer increased with the oxygen content of the discharge then became fairly constant at high O2 concentrations while the etch rate of the underlying dielectric film (SiN) was proportional to the Freon 14 content. This new polymer shows little loading effect. A 1:1 etch rate ratio of SiN to PC-1500 was established for good planarity.