BY ZULHILMI ZAINAL Follow on Twitter
The regulation time of the match, which was held at the Changzhou Olympic Sports Centre, had ended tied at 2-2.
Park Hang-seo's men produced the win against Qatar despite going behind twice in the match.
The West Asian side opened the scoring in the 39th minute, a penalty that was converted by Akram Afif after Bui Tien Dung fouled a Qatar player in the danger area.
But the Southeast Asian side clawed their way back into the match, and could have found the equaliser in the 66th minute through a freekick from inside the Qatar penalty box.
It was given by the referee when goalkeeper Mohammed Al Bakari picked up a backpass. However, mercurial midfielder Nguyen Quang Hai could only hit the crossbar with his effort.
But Quang Hai made up for it just a minute later, pouncing first on a defensive mix-up to draw the scoreline level.
Qatar however retook the lead with just three minutes remaining on the clock, with Almoez Ali squeezing in a shot from near the Vietnam goalline, following an attempt that was not contained properly by the defenders.
The Golden Star would not be unnerved, and Quang Hai restored parity again just one minute later to rescue them. Receiving the ball just outside the Qatar penalty box, he shifted the ball to his left, before curling a shot just beyond the reach of Al Bakari.
Extra time produced no goal for either side, and Vietnam again had to settle their encounter through penalty shootout.
In the quarter-final stage they had edged out Iraq on penalties, when the match ended tied at 3-3.
This time around, Quang Hai made their fans who were present at the stadium nervous, when his shot, Vietnam's first, was saved by Al Bakari.
However, Vietnam goalkeeper Bùi Tien Dung eliminated Qatar's penalty lead in the following kick, saving Ahmad Moein's shot.
Both sides then scored their penalties, until Tien Dung kept out Sultan Al Brake, Qatar's fifth penalty. Vu Van Thanh then kept his nerves to convert Vietnam's fifth shot, and send the 2017 World Cup U-20 participants through to the final.
In the tournament decider which will be played this Sunday, they will face either Uzbekistan or Korea Republic, whose semi-final encounter was still taking place at the time of publication.