Thermal conductivities of InSb and GaSb in solid and liquid states were measured with a ceramic probe. Thermal conductivities at melting points were about 17.7 (W/mK) at 803 K for molten InSb and 21.7 (W/mK) at 993 K for molten GaSb. Thermal conductivities were slightly increased with increasing temperature in liquid state. Lorenz numbers in liquid state were 2.34×10−8(W&OHgr;/K2) at 803 K for InSb and 2.07×10−8(W&OHgr;/K2) at 993 K for GaSb.