Positron annihilation and electron spin resonance (ESR) have been used to study defects introduced by lMeV electron irradiation in n-type cubic silicon carbide (3C-SiC) epitaxially grown on Si by chemical vapor deposition. Positron annihilation measurements by using variable-energy positron beams indicated the narrowing of the Doppler-broadened energy spectrum of annihilation gamma-rays and the decrease in the effective diffusion length of positrons with increasing the electron fluence. These results show the formation of vacancy-type defects in 3C-SiC. An ESR spectrum labeled T1, which has an isotropie g-value of 2.0029±0.0001, was observed in electron irradiated 3C-SiC. The T1 spectrum is interpreted by hyperfine interactions of paramagnetic electrons with 13C at four carbon sites and 29Si at twelve silicon sites, leads that the Tl center results from a point defect at a silicon sublattice site. The production rate of the Tl center was in good agreement with the carrier removal rate, indicating that the Tl center captures an electron from the conduction band. All these results are accounted for by the introduction of negatively charged vacancies at silicon sublattice sites in 3C-SiC by the irradiation.