The New York Stock Exchange’s Dow Jones Industrial Average rose 39 points, or 0.1 per cent, to open at 28,132.
The top 500 indicator for US stocks, the S&P 500, was about two points higher at 3,193.
The tech-heavy Nasdaq index gained almost 10 points to open at 8,839.
Trump on Wednesday became the third president in US history to be impeached when his rival Democrats who control the House of Representatives voted Wednesday to find him guilty of abuse of power and obstruction of Congress after investigations concluding he invited foreign meddling in the US electoral process.
The president will have to face trial in the US Senate but is unlikely to be removed from power as the higher legislative decision-making body is controlled by members of his Republican party, who have made it clear that they viewed his impeachment as a sham.
US stocks have had one of the biggest and most prolonged bull runs in years, inspired by runaway jobs growth and other strong economic data as well the recently-concluded US-Mexico-Canada-Agreement (USMCA) and, more recently, moves to resolve the US-China trade dispute.