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In this letter, we report results of direct current (dc) and radio-frequency (RF) characteristics of self-assembled InAs quantum-dot (QD) electrooptic modulators. Although dc modulation results have been reported in the literature, these are the first high-frequency designs and measurements. These QD modulator wafers were grown by molecular beam epitaxy (MBE) and phase modulator devices were fabricated with coplanar traveling-wave electrodes. For the 800-μm-long modulators, the half-wave voltage Vπ was measured as 11.4 V at 1.55 μm and 7.34 V at 1.32 μm. The phase variation is 21.9°/(mm·V). The linear electrooptic coefficient T41 is calculated to be 35.4 pm/V for QDs. These modulators have a 3-dB bandwidth of 10 GHz. A signal-to-noise ratio of 9 dB was measured at 20 GHz.