President Tsai visited Hawaii at the weekend on her way to three of Taiwan's diplomatic allies in the Pacific despite China, which considers Taiwan a wayward province, calling on the United States to stop the trip.
Her trip comes less than two weeks before President Donald Trump visits Beijing.
China has increased the pressure on Taiwan since President Tsai took office last year, suspecting she wants to push for its formal independence, by conducting more military drills around the island and slowly peeling away its few remaining diplomatic allies.
President Tsai described Taiwan-US relations as being "unprecedentedly friendly" in comments released by Taiwan's presidential office on Monday.
"We are happy to see US promises of peace and stability for the Asia-Pacific region, and from meetings with the United States understand the necessity to increase investment in defence," it quoted her as saying.
Taiwan has raised defence spending considerably this year and will continue to do so, she said while meeting two US think tanks.
The United States and Taiwan have not had formal diplomatic relations since Washington established ties with Beijing in 1979, but the United States is bound by law to provide Taiwan with the means to defend itself.
Taiwan is well armed with mostly US-made weapons but has been pushing for sales of more advanced equipment, such as fighter jets, to deal with what Taipei sees as a growing threat from China and its own rapidly modernising armed forces.
China has never renounced the use of force to bring Taiwan under its control. It regularly calls Taiwan the most sensitive and important issue between it and the United States and has been upset by US moves to expand military exchanges with Taiwan and continued US arms sales to the island.
President Tsai's stopover in Hawaii included a tour of a Pearl Harbor memorial, a banquet with the overseas Taiwan community, and joint speeches with Ambassador James Moriarty, the chairman of the US Mission in Taiwan, also known as the American Institute in Taiwan.
It was her second US visit this year. In January, President Tsai stopped in Houston and San Francisco on her way to and from Latin America.
President Tsai moves on to visit the Marshall Islands, Tuvalu, and the Solomon Islands from Monday during a week-long trip and will stop over in the US territory of Guam on her way back to Taiwan.