AbstractAn electrostatic sheath formation on carbon and molybdenum target plates for plasmas with electrons of two different temperatures is analyzed by a simple formulation including the effect of secondary electron emission from the target plate. A modified Bohm criterion is given in terms of effective electron temperature which defines the ion sound velocity in two component plasmas. Hot electrons and the associated secondary electrons greatly modify the charge balance in the sheath. They change the sheath voltage and consequently the heat transmission characteristics. A critical amount of hot electrons for sharp increase in the sheath voltage is given by a simple formula.