Les Verts, who extended their unbeaten run to 17 matches in all competitions this year, have 54 points with six games left as they cling on to the final qualifying spot for a place in Europe's elite club competition next season.
Fourth-placed arch-rivals Olympique Lyon, who host mid-table Toulouse on Sunday having lost their last three games, are one point behind while Lille, in fifth, are a further point back before welcoming second-placed Olympique Marseille on Sunday.
"We could have won this game in the first half but after the break we just sat back," St Etienne defender Jonathan Brison told TV channel BeIN Sport.
"It's a good result because we remain unbeaten," he added.
Les Verts, who have not lost in their last 13 Ligue 1 games, struggled to unsettle a defence that was desperate to tighten up after conceding seven goals in the last two matches.
It was St Etienne who had the first chance after 15 minutes when Pierre-Emerick Aubameyang intercepted a poor back pass from Rudy Mater but the Gabon striker skied his attempt.
Valenciennes, who have now won only one of their last 13 league games, had a great chance in the 28th but Gael Danic's curled shot from the edge of the box was tipped over by Stephane Ruffier.
The second half was even less exciting than the first with neither side able to create any decent opportunities.
The draw left Valenciennes in 13th place on 37 points.
"It's a good result even if we wanted to win at home. We made a lot of effort," Valenciennes defender Gaetan Bong told BeIN Sport.
"The most important thing is that we did not concede any goals."
On Saturday, Paris St Germain will aim to stretch their lead at the top to 10 points with a win at bottom side Troyes.
Champions Montpellier, who are seventh on 48 points, visit mid-table Girondins Bordeaux.