Shiva (60kg) and Sumit Sangwan (91kg) stunned higher rated opponents to enter the final of their respective weight categories at the Asian Boxing Championships here on Friday.
The fourth-seeded Thapa upset Olympic bronze medallist and top seed Dorjnyambuug Otgondalai of Mongolia 3-2 in the semi-finals of the Lightweight (60kg) category.
The Assam lad will fight Elnur Abduraimov of Uzbekistan for the gold medal. Abduraimov defeated China's Jun Shan in his semi-final bout.
Sumit, on the other hand, clinched a comprehensive 5-0 victory over second seed Jakhon Qurbonov of Tajikistan in the last four stage of the Heavyweight (91kg) division.
However, top seed Vikas Krishan settled for a bronze medal in the middleweight (75kg) category after he gave a walkover in the semi-finals to fourth seed Lee Dongyun of South Korea.
With two silver medals assured, Indian boxers surpassed their performance from the last edition of the continental event in 2015 when they had taken three medals including a silver and two bronze.