Provided are an electro-optic device with a high modulation rate and a mach-zehnder optical modulator having the same. The electro-optic device includes a slap, a rip waveguide, a first impurity region, a second impurity region, and a third impurity region. The slap is disposed on a substrate. The rip waveguide includes a mesa extending in one direction on the slap and the slap disposed under the mesa. The first impurity region is disposed in the slap of one side of the mesa. The third impurity region is disposed in the slap of the other side of the mesa to oppose the first impurity region. The second impurity region is disposed in the rip waveguide between the first impurity region and the third impurity region.