Wash the salmon fillets thoroughly and place in a pan. In a large bowl, combine soy sauce, olive oil, garlic, ginger, and sugar and mix well. Pour the marinade over the fillets. Refrigerate for 4 to 6 hours.
Preheat a smoker to 250 degrees F with hickory chips.
Place salmon on the smoker. Smoke for 60 to 90 minutes, or until fish flakes nicely.
*Note: If fish is skinless, cook on foil
Serve with freshly squeezed lemon just before serving.