Line two baking sheets with parchment and set a fork or dipping tool nearby. Make sure the mini pretzels are dry and ready.
Place the finely chopped semisweet chocolate in a large heatproof bowl. Set aside about one-third of it (roughly 4 ounces) as seed chocolate for tempering.
Set the remaining two-thirds of the semisweet chocolate over a pot of barely simmering water (bowl should not touch the water). Stir gently until melted and 113–120°F, 5–8 minutes. Remove the bowl from heat.
Gradually add the reserved seed chocolate, stirring until mostly melted and the chocolate cools to 88–90°F, 5–10 minutes. If a few small bits remain, remove them. Test temper by dipping a tip of a mini pretzel; it should set firm and glossy at room temperature within 3–5 minutes.
Working one at a time, dip mini pretzels into the tempered chocolate, turning to coat. Lift out with the fork, tap the fork on the bowl’s edge to let excess drip off, and place on the parchment. Repeat with remaining mini pretzels.
Let the chocolate set at room temperature until firm and snappy, 15–30 minutes. If you did not temper the chocolate, refrigerate trays 10–15 minutes to set, then keep chilled to prevent bloom.
Once set, transfer chocolate-covered mini pretzels to an airtight container, separating layers with parchment. Store at cool room temperature up to 1 week (tempered) or refrigerated up to 1 week (untempered).