Elon Musk defied the challenges of the coronavirus pandemic to help Tesla Inc. deliver a wildly successful year. For 2021, the chief executive is setting expectations even higher and has the long-haul trucking industry in his sights.

Having demonstrated that consumers will enthusiastically buy electric cars, Mr. Musk now wants to show the trucking industry—a risk-averse and thin-margin business with little patience for Silicon-Valley hype—will embrace a battery-powered vehicle.

The Tesla semitrailer truck is part of a flurry of vehicle-production activity Mr. Musk has planned for 2021. Those plans include a new electric pickup truck, factories in Berlin and Texas starting up, and higher output at the company’s Shanghai plant. Tesla is aiming to produce at least 68% more vehicles across its inventory next year, Mr. Musk has suggested, from the 500,000 car deliveries the company targets in 2020.

Investors have a lot riding on Tesla’s new projects going smoothly. The company’s stock has more than quintupled since the start of the year, buoyed by five sequential quarterly profits that put it on track for its first-ever full-year in the black. The stock trades at more than 16 times annual sales, far more than its peer auto makers, and is poised to be added to the S&P; 500 index in December.

The Semi, to be built at Tesla’s Austin, Texas, factory, and due to customers starting next year, will be a new challenge for the Silicon Valley electric-car maker. It will test how far Tesla has come with battery improvements it teased in September, how far it can push its manufacturing capabilities and whether the company can break into a new industry where Mr. Musk’s star power has less pull among buyers primarily concerned about price and practicality.