The critical temperature, critical compressibility factor and the inversion temperature of cesium, rubidium and potassium are correlated through the generalized van der Waals equation of state. This three-parameter equation differs from the known van der Waals equation of state by the modified attractive term. For cesium, rubidium and potassium, the reduced inversion temperature and its ratio to the critical compressibility factor were estimated. The results of estimation were in agreement with experimental data. It has been established that cesium, rubidium and potassium obeyed the single-parameter law of corresponding states with the reduced inversion temperature or its ratio to the critical compressibility factor as the thermodynamic similarity parameter.