The effect of different substituents on stability of several N-heterocyclic silylenes study with the aid of ∆ES-T parameter at DFT using B3LYP/6-311++G** basis set. The field of stable silylene research has grown dramatically since the first isolation of a stable silylene in 1994. Prior to 1994, silylenes existed only as reactive intermediates, isolable only in low temperature matrixes. Since then, several stable silylenes have been synthesized, some in fact showing remarkable thermal stability. Here, silylens with electron donating groups have stability higher than electron withdrawing ones.