Preheat oven to 450°F.
Arrange the sausages, potatoes, onion wedges, peppers, and rosemary in one layer on a half-sheet pan. Drizzle with olive oil and sprinkle with salt, paying particular attention to the vegetables (the sausages are already seasoned); gently toss to coat.
Roast for 30 to 35 minutes or until potatoes are fork-tender and sausages are lightly browned, stirring once halfway through roasting.