Temperature distributions and local heal transfer coefficients were measured with shielded thermocouple probes and a heat flux meter, respectively. The measurements were carried out in the combustion chamber of a 12-MW(th) circulating fluidized bed (CFB) boiler. Effects of the bed bulk temperature, the suspension density, the superficial gas velocity, and the shape of the heat transfer surfaces on the temperature distribution and heat transfer coefficient were investigated. The results indicate that the heat transfer coefficient increases with increasing bulk bed temperature, superficial gas velocity, and suspension density. The thermal boundary-layer thickness decreases with increasing gas velocity, while the bulk bed temperature has only a small influence on it. The shape of the heat transfer surfaces affects particle motion near the wall, as a result of which differences appear in the heat transfer coefficient and thermal boundary layer. The results were compared with available experimental data in the literature, and good agreement is mostly found.