Band‐to‐band Auger recombination in InGaAsP lasers is studied theoretically. An approximation method for the calculation is derived and the Auger coefficient is given explicitly as a function of injected carrier density. Auger lifetime and the threshold current density for the InGaAsP laser are calculated with good agreement with reported experimental results. This shows that Auger recombination is one of the dominant factors which causes the poor temperature characteristics of InGaAsP laser threshold current.