Modulation characteristics of lattice-matched InGaAs-InP MQW structures containing 50 and 150 wells are compared. A contrast ratio of 2.6:1 (4.1 dB) has been attained at 1590 nm (4.9 dB insertion loss) in a 150 well sample. This is the largest perpendicular-geometry modulation reported in InGaAs-InP to date. A 46 meV quantum-confined Stark shift has been attained in an applied electric field of 2.5 × 105V/cm−1in the 50 well sample. This shift is ̃ 8 times the exciton binding energy, and is larger than any previously reported in InGaAs-InP.