We report a pre-amplifying junction field effect transistor (JFET) module on a chip for cryogenic applications such as bolometer and X-ray microcalorimeter. In order to maintain the optimum performance of the JFETs at 130 K, the module has built-in aluminum micro-heaters while the JFETs are thermally isolated from a heat sink. The thermal isolation is achieved by suspending a micromachined silicon support platform (6 μm thick) with polyimide wires. A layer of aluminum electrodes is patterned on top of the polyimide wires for electrical contacts and on top of the silicon platform for the heaters. This process involves reactive-ion-etching (RIE) of silicon and polyimide, patterning of aluminum electrodes over the polyimide, back side deep-reactive-ion-etching (DRIE) of silicon, and releasing of the modules. In this paper, we describe a micromachining process of the JFET modules on silicon-on-insulator (SOI) wafers.