Add the pineapple juice, soy sauce, ketchup, brown sugar, salt, minced garlic, ginger, and garlic powder to small bowl and whisk well until the marinade it combined.
Add the chicken thighs to a Ziploc bag, and pour the marinade over the chicken thighs. Seal the bag, place evenly in a pan being sure that all the chicken is coated, and marinate in the fridge for at least 2 hours.
Preheat the grill to medium-high heat, around 450°F.
Remove the chicken from the bag and place directly onto the grill grates.
Grill for 5-10 minutes on each side until the internal temperature of the chicken reaches at least 165°F.