A laser specklegram technique has been developed and applied to directly measure the wall temperature gradient for convective heat transfer problems. This relatively new technique has several advantages for heat convection measurements over conventional techniques, which usually require laborious corrections to account for the radiation and conduction heat losses. The specklegram technique provides extremely high resolution for the evaluation of local quantities, and a full-field information can be obtained by photographically recording a single specklegram. Satisfactory measurement accuracy of the technique has been demonstrated when applied to a thermal layer along a vertical isothermal wall and a vertical channel flow between paralle isothermal channel. The technique has also been used to investigate a new problem: the dependence of heat transfer characteristics of converging channel flows on different inclination angles. The optimal exit opening ratio of the converging channel, (b/L)opt corresponding to maximum NuL is determined as 0.07, 0.1, 0.3, 0.35, and 0.4 for each of 0, 15, 30, 45 and 60 deg inclination angles measured from the vertical.