On-line aging monitoring is the basis for high reliability operation of converters because many converter failures are related to aging defects. Conventional aging monitoring methods mainly focus on a single semiconductor device or module, and their industrial applications are limited. First, several aging monitoring circuits are required in a converter, which raises the cost. Second, the converter structure has to be modified, which is impractical. To solve this problem, a converter-level aging monitoring method is proposed in this paper, which is based on the on-line extraction of DC-link bus leakage current. The monitored aging mode of the proposed method is Si material degradation, which is one of the chip-related aging defects. First, the DC bus leakage current is analyzed theoretically as an indicator of the Si material degradation. A corresponding description parameter d Sicon is proposed. Second, an on-line measuring method is proposed for the DC bus leakage current, which is called the state-selection method. Third, a converter-level Si material degradation monitoring strategy is proposed. On-line experiments based on a constant-voltage-constant-temperature (CVCT) accelerated aging test verify the effectiveness of the proposed method.