1. Voltage Platform & Technology: The STP23N80K5 (800V MDmesh™ K5) is optimized for higher voltage and higher frequency switching, featuring significantly lower Ciss (1000pF vs. 1765pF). This results in lower switching loss and reduced noise in high-frequency applications such as SMPS. The FCP13N60N (600V SupreMOS™), on the other hand, is optimized for a balance between Rdson and cost at medium voltage levels. 2. On-Resistance & Test Conditions: Although the Rdson of the FCP13N60N appears lower (258mΩ @ 6.5A), its test current is only 81% of that for the STP23N80K5 (280mΩ @ 8A). In practice, under conditions close to rated current, the K5 technology may demonstrate better high-temperature Rdson stability. 3. Gate Charge & Drive Requirements: The FCP13N60N has 20% higher Qg (39.5nC vs. 33nC). Combined with its higher Ciss, this means that at the same switching frequency, it will require higher drive current or result in slower switching speed, potentially impacting efficiency. 4. Implied Thermal Resistance Difference: The significantly higher Pd (190W) of the STP23N80K5 indicates lower package thermal resistance or greater die thermal capacity. Under equivalent cooling conditions, it can sustain higher continuous power dissipation. Thermal performance must be rechecked if substitution is attempted. Substitution Recommendation: Replacement may be considered if actual operating conditions are Vds < 500V, Id < 10A, and switching frequency is below 50kHz, provided that drive circuit margin and thermal headroom are verified. Direct substitution is not recommended for high-frequency, high-voltage topologies such as quasi-resonant or LLC converters.