This study describes the development of an evaluation method of uncertainty in temperature measurement of surface-mounted components by several types of thermocouples. When thermocouples conduct the temperature measurement of the surface-mounted components, the components’ temperature decreases because the thermocouples dissipate heat like a pin fin. Temperature measurement techniques for miniaturized electrical components are strongly needed to ensure the operation’s guaranteed temperature. In this report, a heat transfer experiment around thermocouples installed on the surface of the PCBs was conducted while changing the type and the mounting angle of thermocouples. Through the temperature measurement, the decrease of the temperature around the thermocouples was confirmed.