Purpose: This study was conducted to investigate the antimicrobial effect of an 809-nm semiconductor laser on common dental implant surfaces. Materials and Methods: Sandblasted and acid-etched (SA), plasma-sprayed (TPS), and hydroxyapatite-coated (HA) titanium disks were incubated with a suspension of S sanguinis (ATCC 10556) and subsequently irradiated with a gallium-aluminum-arsenide (GaAlAs) laser using a 600-µm optical fiber with a power output of 0.5 to 2.5 W, corresponding to power densities of 176.9 to 884.6 W/cm2. Bacterial reduction was calculated by counting colony-forming units on blood agar plates. Cell numbers were compared to untreated control samples and to samples treated with chlorhexidine digluconate (CHX). Heat development during irradiation of the implants placed in bone blocks was visualized by means of shortwave thermography. Results: In TPS and SA specimens, laser irradiation led to a significant bacterial reduction at all power settings. In an energydependent manner, the number of viable bacteria was reduced by 45.0% to 99.4% in TPS specimens and 57.6% to 99.9% in SA specimens. On HA-coated disks, a significant bacterial kill was achieved at 2.0 W (98.2%) and 2.5 W (99.3%) only (t test, P .05). For specimens treated with CHX, the bacterial counts were reduced by 99.99% in TPS and HA-coated samples and by 99.89% in SA samples. Discussion: The results of the study indicate that the 809-nm semiconductor laser is capable of decontaminating implant surfaces. Surface characteristics determine the necessary power density to achieve a sufficient bactericidal effect. The bactericidal effect, however, was lower than that achieved by a 1- minute treatment with 0.2% CHX. The rapid heat generation during laser irradiation requires special consideration of thermal damage to adjacent tissues. Conclusion: No obvious advantage of semiconductor laser treatment over conventional methods of disinfection could be detected in vitro.