Gale, 28, beat Wales' Lauren Price to guarantee at least silver in her first major international tournament.
She will face France's Maily Nicar on Wednesday as she attempts to emulate Nicola Adams and become only the second female boxer from Great Britain to win gold at the European Championships.
GB pair Sandy Ryan and Lisa Whiteside joined Price in winning bronze medals.
Lightweight Ryan lost a unanimous decision to Olympic bronze medallist Mira Potkonen of Finland, while flyweight Whiteside lost in the same fashion to Russia's Elena Saveleva.
England's Natasha Gale has reached the middleweight final of the European Women's Boxing Championships in Sofia.