Ms Pelosi – the most senior US politician to visit in 25 years – departed on Wednesday after meeting leaders in the capital Taipei.
But her visit, as part of a wider Asian tour, sparked fury in Beijing after she ignored its warnings not to travel to the island.
Taiwan is self-ruled – but China sees it as a breakaway province that will eventually unite with it.
Accusing the US of “violating China’s sovereignty under the guise of so-called democracy”, Chinese Foreign Minister Wang Yi said: “Those who play with fire will not come to a good end and those who offend China will be punished.”
In a statement following the visit, Ms Pelosi said China cannot “prevent world leaders or anyone from traveling to Taiwan to pay respect to its flourishing democracy, to highlight its many successes and to reaffirm our commitment to continued collaboration”.
The senior US Democrat’s visit was not approved by her party colleague, President Joe Biden, who had said the American military felt it was “not a good idea right now” amid heightened tensions between the two countries.
The US walks a diplomatic tightrope with its Taiwan policy. On the one hand, it abides by the “One China” policy, which recognises only one Chinese government, giving it formal ties with Beijing and not Taiwan.
On the other, it maintains a “robust unofficial” relationship with the island, which includes selling weapons for Taiwan to defend itself.
As speaker of the US House of Representatives, Ms Pelosi is second in line to the US presidency, behind Vice-President Kamala Harris.
In response to the trip, China announced what it called “necessary and just” military drills in seas around 10 miles (16km) from Taiwan.
The exercises – which will begin on Thursday and last for five days – will take place in some of the world’s busiest waterways and will include “long-range live ammunition shooting”.
China’s defence ministry has admitted that some exercises may breach Taiwan’s territorial waters. In recent days, Chinese warplanes ventured as far as the median line, the unofficial divide separating China and Taiwan in the waters between them.
Taiwan has asked ships to find alternative routes to avoid the drills and is negotiating with neighbouring Japan and the Philippines to find alternative aviation routes.
President Tsai Ing-wen said the country was facing “deliberately heightened military threats”.
In an effort to calm the situation, the foreign ministers from the G7 nations – Canada, France, Germany, Italy, Japan, the UK and US – released a joint statement saying China’s escalation risked destabilising the region.
“There is no justification to use a visit as pretext for aggressive military activity in the Taiwan Strait. It is normal and routine for legislators from our countries to travel internationally,” the statement said.
