Helium gas is commonly used as heat transport fluid in high temperature energy system due to its advantage of inert gas. For designing a compact heat exchanger for such high temperature energy systems, pressure drop and heat transfer characteristics of high temperature and high pressure helium flow in small hydraulic diameter channels, so called minichannels, are in need. In this study, measurement of convective heat transfer coefficients of single phase helium gas flow through a circular minichannel has been conducted to investigate the effect of high pressure and high temperature conditions. The main objective of the present work was to study the surface temperature measurement technique using thermocouples and its effect on the accuracy of the measured convective heat transfer coefficient. The measured convective heat transfer coefficients inside the tube are discussed in terms of surface temperature measurement technique and deviations from the predictions of existing heat transfer correlations.