Cut the chicken thighs into halves and place them into a bowl. Season them with the garlic salt and pour the ranch dressing on top. Using your hands, massage the chicken until the seasoning is evenly coated. Cover the bowl with plastic wrap and allow the chicken to marinate for at least 6 hours (overnight preferred).
Preheat the grill on high (about 380°F). Grill chicken on both sides until golden brown and the internal temperature reaches 165°F. Serve and enjoy!