Long-term 100/spl deg/C and 85/spl deg/C biased aging tests on OC48 x-cut lithium-niobate optical intensity modulators have been run for four years. The 100/spl deg/C test results clearly show that the bias voltage does not exhibit the conventional catastrophic growth curve, but rather peaks between 10 000 and 35 000 h at levels well below typically used bias voltage rails (/spl plusmn/12 V). This promises a very high reliability for these x-cut lithium-niobate modulators for long-term bias-drift failure mode. Using the data, a bias-drift failure rate under ordinary operation conditions, 20 years at 40/spl deg/C, is estimated to be <1 failures in time with activation energy of 1.2 eV.