A wafer holding body used for a wafer prober for testing a semiconductor wafer includes a chuck top having a conductive layer on a surface thereof and a support body supporting the chuck top. The support body has a base portion opposing the chuck top and a side portion extending from the perimeter of the base portion to the chuck top to support the chuck top. A cavity portion is formed between the chuck top and the base portion of the support body. A reflection plate is provided in the cavity portion. A heater unit and a wafer prober includes the wafer holding body.