Reactive sticking coefficients (RSC) of silicon hydride radicals are evaluated, between 853 and 903 K, from simulating the film thickness contours of trenches deposited in a SiH4/Ar reaction system. The RSC values of SiH4, Si2H6 and Si3H8, calculated from the hydrogen desorption kinetics and the surface hydrogenation kinetics at each trench location, are used to estimate their contributions in film growth. The radical RSC values and concentration are the fitting parameters in the trench simulation, in which the sum of SiH4, Si2H6 and Si3H8 contributions is referred to a film-forming species of low sticking coefficient, and the radicals as the other species of high sticking coefficient. The correlated RSC value of the radicals, generally less than 1, is higher than that of silane by approximately five orders of magnitude. The radical RSC linearly increases with the surface fraction of dangling bonds theta. The extrapolated RSC value at theta = 1 is unity, which suggests that a radical has probability of reaction with dangling bonds of unity. The deviation from this idealized value is due to a large percentage of the growing surface being hydrogen-passivated. The probability of the reaction of a radical with the hydrogen-terminated surface, which is extrapolated at theta = 0, has an activation energy of 4.6 kcal/mol.