The hole subband structures and effective masses of tensile strained Si/Sil-yGey quantum wells are calculated by using the 6 × 6 k.p method.The results show that when the tensile strain is induced in the quantum well,the light-hole state becomes the ground state,and the light hole effective masses in the growth direction are strongly reduced while the in-plane effective masses are considerable.Quantitative calculation of the valence intersubband transition between two light hole states in a 7nm tensile strained Si/Si0.55Ge0.45 quantum well grown on a relaxed Si0.5Ge0.5(too)substrates shows a large absorption coefficient of 8400cm-1.