A Mach-Zehnder electro-optic modulator is designed and fabricated based on upper-clad GeO2-doped silica ridge waveguides with thermal poling. The electro-optic coefficient obtained is about 0.05 pm/V and is polarizationinsensitive. An extinction ratio of over 17dB is achieved. The transmission loss of the modulator for the TE mode is 2-3 dB higher than that for the TM mode after the poling.