Abstract: A GaAs semiconductor device comprising a FET (field effect transistor), and a low dielectric constant passivation. The passivation protects the surface of the active area of the FET under the FET. The FET is a high electron mobility transistor or a pseudomorphic high electron mobility transistor. The passivation is formed by spin coating and made of a low dielectric constant compound. The low dielectric constant compound is Benzocyclobutene. Advantages are a simple manufacturing process, fewer surface defects, and improved device performance. Therefore, a superior device is provided at a reduced production cost.