The trapping of neutrinos in strong gravitational fields is considered. The zero-mass Dirac equation for curved space-time is specialized to the case of a static spherically symmetric object of constant density. The WKB method is applied to obtain the energy spectrum of the semibound states of the neutrinos. The probability of penetration through the barrier presented by the gravitational field is calculated for each level and the lifetime of a neutrino in the well obtained. It is shown that in the energy domains of interest the classical approximation is applicable and the total fraction of neutrinos trapped after emission is obtained. It is shown that neutrino trapping may take place in neutron stars with stiff equations of state.