  We report on the first demonstration of long-term thermally stable
silicon-organic hybrid (SOH) modulators in accordance with Telcordia standards
of high-temperature storage. The devices rely on an organic electro-optic
sidechain polymer with a high glass transition temperature of 172 {\deg}C. In
our high-temperature storage experiments at 85 {\deg}C, we find that the
electro-optic activity converges to a constant long-term stable level after an
initial decay. If we consider a burn-in time of 300 h, the {\pi}-voltage of the
modulators increases on average by less than 15 % if we store the devices for
additional 2400 h. The performance of the devices is demonstrated by generating
high-quality 40 Gbit/s OOK signals both after the burn-in period and after
extended high-temperature storage.
