Pat the chicken tenders dry with paper towels and set aside.
In a large bowl, whisk together 2 cups all-purpose flour and 1½ teaspoons salt.
In a separate bowl or large measuring cup, stir 2 cups water and 3 tablespoons vinegar until combined.
Sprinkle 1½ teaspoons baking soda into the water–vinegar mixture (it will foam). Immediately pour the foaming mixture into the flour mixture.
Gently stir the batter until just combined — small lumps are fine. The batter should be thin enough to coat the tenders; do not overmix.
Pour oil to a depth of 2 inches into a large Dutch oven or deep skillet and heat to 350°F (use a thermometer).
Working in small batches, dip each chicken tender into the batter, letting excess drip back into the bowl.
Carefully add battered tenders to the hot oil without overcrowding. Fry each batch about 4–6 minutes (about 5 minutes) until golden and the chicken is cooked through.
Transfer fried tenders to a paper towel–lined plate to drain and rest briefly.
Serve the tempura chicken fingers hot with your favorite dipping sauces.