This paper reports the effect of annealing on hydrogenated amorphous silicon films (a-Si : H) deposited by r.f self-bias technique on cathode in an asymmetric r.f. plasma CVD system at room temperature. Detailed study of the variation of the dark and photoconductivity (sigma(D) and sigma(ph)) as a function of temperature and light intensity, surface morphology, hydrogen evolution, optical absorption, subgap absorption and related parameters, thermal and structural disorder on the optical-absorption edge, IR vibrational modes and bonded hydrogen content have been carried out on unannealed and annealed samples at different temperatures (T-a) from 100 degrees C to 550 degrees C. It is found that the values of sigma(ph) increase and that of Urbach energy (E-o), subgap defect density (N-d) and the polyhydride to monohydride ratio decrease upto T-a = 250 degrees C and beyond 250 degrees C the values of sigma(ph) decrease and that of E-o, N-d and the polyhydride to monohydride ratio increase. The best opto-electronic properties with much improved sigma(ph) and sigma(ph)/sigma(D) and dominant monohydride bonding are obtained after annealing the room temperature deposited film at 250 degrees C for 1 h. The sigma(D) data obeys a Meyer Neldel rule in annealed a-Si : H films. The value of optical band gap is found to be related to the E-o and the hydrogen content. The Urbach energy (E-o) which is a measure of the disorder is the sum of structural and thermal disorder. The structural disorder part decreases with the annealing temperature upto similar to 300 degrees C and thereafter it increases. The curves of optical absorption coefficient versus photon energy at different T-a converge to a common point.