Effects of neutron radiation on electrical properties of Si detectors have been studied. At high neutron fluence (phi-n greater-than-or-equal-to 10(12) n/cm2), C-V characteristics of detectors with high resistivities (p greater-than-or-equal-to 1 k-OMEGA cm) become frequency dependent. A two-trap level model describing this frequency dependent effect is proposed. Room temperature anneal of neutron damaged (at LN2 temperature) detectors shows three anneal stages, while two anneal stages were observed in elevated temperature anneal.