Here we describe the evolution of a silicon, MEMS-based chip design developed for infrared gas and chemical detection. The “Sensor-Chip,” with integrated photonic crystal and reflective optics, employs narrow-band optical emission/absorption for selective identification of gas and chemical species. Gas concentration is derived from attenuated optical power, which results in a change in device set point. This change in temperature results in a change in device resistance, via the TCR of the Si. Thermal non-uniformity across the device results in optical “noise” and accelerates localized thermal and electrical failures. This paper reports the influence of processing and design, on achieving uniformly heated, high reliability devices. Specifically, we examine the role of contacts, drive scheme, and device thermal distribution on chip design. Experimentally the temperature uniformity was characterized using an infrared camera. Experimental results indicate that the design of the contact areas in combination with the device design is essential for the reliable performance of the Sensor-Chip. Redesigned devices were fabricated and demonstrated as highly-selective gas and chemical sensors.