The thermal expansion of the crystal lattices of germanium, silicon, and the alloys InSb and GaAs has been measured by the hightemperature X-ray diffraction method. The coefficients in the expansion equation αt=α0(1+αt+βt2+γt3+δt4)for the materials investigated were found to be as follows: Germanium (99.9999% purity, in the temperature range 0-900℃): α=5.019×10-6, β=1.230×10-9, γ=5.420×10-12, δ=-4.000×10-15 and α0, the lattice parameter at 0℃, is 5.64573 kX. Silicon (99.9999% purity, 0-900℃): α=3.893×10-6, β=-2.101×10-9, γ=5.125×10-12, δ=-1.833×10-15 and α0=5.41921 kX. InSb (zone-refined, 0-500℃):α=5.724×10-6, β=-0.036×10-9, γ=-0.050×10-12, δ=0.166×10-15 and α0=6.46420 kX. GaAs(zone-refined, 0-750℃): α=6.174×10-6, β=0.140×10-9, γ=-1.425×10-12, δ=2.282×10-15 and α0=5.64037 kX. The lattice parameters at various temperatures calculated with these constants are in excellent agreement with the observed values.