on the first n type inp buffer layer 60 by 20 mev or more in such production process steps of the semiconductor laser with light modulator of this third embodiment in a state where the first n type inp buffer layer 60 is formed on the n type inp substrate 1 after the stripe shaped recess 1b is formed and the n type gainp layer 2 fills the recess 1b the second n type inp buffer layer 70 the undoped ingaasp layer 4 and the p type inp layer 5 are epitaxially grown in this order therefore when the first n type inp buffer layer 60 is for example 0 9 u03bcm thick simply by growing the second n type inp buffer layer 70 the undoped ingaasp layer 4 and the p type inp layer 5 on the first n type inp buffer layer 60 with thicknesses of 0 1 u03bcm 0 1 u03bcm and 0 5 u03bcm respectively the operating layer of the semiconductor laser can be produced in a thickness that realizes a stable laser oscillation i e 1 5 u03bcm or more as described above and the operating layer of the light modulator can be produced to have a thickness of approximately 0 7 u03bcm therefore in the production process steps of the semiconductor laser with light modulator the ga composition of the n type gainp layer 2 is within a range of 0 047 to 0 064 the difference in the energy band gap between the active layer of the semiconductor laser and the.