The objective of this book is to study the optical properties of silicon, as a function of temperature, in the infrared range of wavelengths. The wavelength range, considered in this study, is between 1 micron and 20 microns. The temperature range observed is from 50 degrees Celsius to 1000 degrees Celsius. Varying wafer thickness and doping are taken into account. The thickness of the native oxide, silicon dioxide, must be taken into account as well as its orientation (front side versus back side). The effect of layering wafers one onto another is investigated. It is shown that all these parameters affect the optical properties, emittance, reflectance, and transmittance, of a wafer and multiple layers of wafers. The IR-563 Blackbody source is utilized as the infrared source. Emissivity measurements are performed using an Ex-Series FLIR camera and a Laser Grip -Model 1022. A matrix method based approach is implemented to simulate the optical properties.