In a small bowl, combine kosher salt, black pepper, smoked paprika, garlic powder, onion powder, dried thyme, and dried oregano.
Pat the chicken thighs dry with paper towels. Rub the spice mixture evenly over all sides of the chicken thighs.
Heat olive oil in a large skillet over medium-high heat. Add the chicken thighs skin-side down and sear for 3-4 minutes until the skin is golden brown. Flip and sear the other side for 2 minutes. Remove from heat.
Place the sliced onion and minced garlic in the bottom of the slow cooker.
Arrange the seared chicken thighs on top of the onions and garlic in the slow cooker.
Pour the chicken broth over the chicken thighs.
Cover and cook on low for 6 hours or until the chicken thighs are tender and cooked through (internal temperature should reach 165°F / 74°C).
Once cooked, remove the chicken thighs and let rest for 5 minutes before serving. Optionally, spoon some of the cooking juices and onions over the chicken for extra flavor.