Pt is a suitable thermistor for use in microbolometers due to its high melting point, chemical inertness, and low 1/f noise. This work explores mechanisms of grain growth to fabricate Pt thin film thermistors for maximizing the temperature coefficient of resistance (TCR). The interplay between the microstructure and TCR is examined by varying Pt film deposition parameters, AlOX interlayer deposition technique, patterning technique, and annealing parameters. A smooth thin film morphology having giant grains of several hundreds of micrometers is achieved by abnormal grain growth, which is not attainable through normal grain growth. The fabrication of thermistor meanders is demonstrated through a combination of processes including Pt film deposition in O2/Ar environment, annealing at 1000 °C in Ar, and ion beam etching. Pt thermistors with a TCR (0 °C – 100 °C) of 0.371 ± 0.001 %/ °C are compatible with microbolometers utilizing carbon nanotube absorbers.