With the increasing penetration of wind power, reliable and cost-effective wind energy production is of more and more importance. As one of the common configurations, the doubly fed induction generator based partial-scale wind power converter is still dominating in the existing wind farms, and its reliability assessment is studied considering the annual wind profile. According to an electro-thermal stress evaluation, the time-to-failure of the key power semiconductors is predicted by using lifetime models and Monte Carlo based variation analysis. Aiming for the system-level reliability analysis, a reliability block diagram can be used based on Weibull distributed component-level reliability. A case study of a 2 MW wind power converter shows that the optimal selection of power module may be different seen from the reliability perspective compared to the electrical stress margin. It can also be seen that the B 1 lifetimes of the grid-side converter and the rotor-side converter deviate a lot by considering the electrical stresses, while they become more balanced by using an optimized design strategies. Thus, the system-level lifetime increases significantly with an appropriate design of the back-to-back power converters.