Prominent among the 23 countries and territories are Canada, the U.S., U.K., South Korea and China, The Thaiger reports.
The extension took effect at the beginning of this month.
Thailand, one of the first countries in Southeast Asia to fully reopen its tourism industry, welcomed about 7.35 million foreigners in the first 10 months of this year. It expects to attract 10 million foreigners this year.
The country is offering 45-day visa-free stay for tourists from over 50 countries including Vietnam.
Vietnam currently offers 30-day single-entry e-visas to citizens of 80 countries and territories, and visa exemption for visitors from 24 countries.
The Vietnamese government has sought recommendations from the tourism, foreign affairs and public security ministries on expanding the list of countries for e-visa issuance.