Sergeant Major Siaw reported to Marine Corps Recruit Depot San Diego, California in April 1993 for recruit training and upon graduation, was meritoriously promoted to the rank of Lance Corporal.  Upon completion of Personnel Administration School in Camp Lejeune, North Carolina, he was assigned to Marine Air Control Squadron 6, 2d Marine Aircraft Wing in Cherry Point, North Carolina.

In June 1997, he reported to Drill Instructor School, Marine Corps Recruit Depot San Diego, California.  He served as a Junior Drill Instructor, Senior Drill Instructor, Marine Corps History Instructor/Curriculum Developer, and Staff Noncommissioned Officer in Charge of the Academic Instruction Unit.  In July 1999, he was meritoriously promoted to the rank of Staff Sergeant, and in September 2000, he was selected as the MCRD San Diego Drill Instructor of the Year.  In October 2000, he was selected as the Commandant of the Marine Corps' Drill Instructor of the Year and meritoriously promoted to the rank of Gunnery Sergeant.  In September 2001, he reported to Marine Aircraft Group 12, 1st Marine Aircraft Wing in Iwakuni, Japan to serve as the Staff Noncommissioned Officer in Charge of the Station Orders Department and Adjutant Chief for Marine Aircraft Group 12.  He was selected to the rank of First Sergeant in December 2003.

In April 2004, he reported to 1st Battalion 3d Marines, 3d Marine Division in Kaneohe Bay, Hawaii to serve as the First Sergeant for Bravo Company, BLT 1/3, 31st Marine Expeditionary Unit.  In June 2004, he deployed in support of the Unit Deployment Program and, subsequently, Operation Iraqi Freedom II for combat operations in Fallujah, Iraq.  In November 2004, he served in Operation Al Fajr/Phantom Fury and, in January 2005, served in combat and security operations for the first Iraqi elections.  In July 2005, he assumed duties as the First Sergeant for Weapons Company, 1st Battalion 3d Marines and deployed in January 2006 in support of Operation Enduring Freedom 6/7 for combat operations in the Pech River Valley of Kunar Province in eastern Afghanistan.  In September 2006, he reported to Military Police Company, Headquarters Battalion, 4th Marine Division in Saint Paul, Minnesota to serve as the Inspector-Instructor First Sergeant, and was selected to the rank of Sergeant Major in November 2006.

In December 2007, he reported for duty as the Sergeant Major for Marine All-Weather Fighter Attack Squadron 121, 3d Marine Aircraft Wing in Miramar, California and deployed in support of the Unit Deployment Program to the Western Pacific.  In September 2009, he reported for duty as the Sergeant Major for 1st Light Armored Reconnaissance Battalion, 1st Marine Division in Camp Pendleton, California and deployed in May 2010 in support of Operation Enduring Freedom 10.1 for combat operations in the Southern Helmand River Valley of Helmand Province, Afghanistan.  In February 2011, he reported for duty as the Sergeant Major for 2d Recruit Training Battalion, and in April 2012, assumed duties as the Sergeant Major for Recruit Training Regiment, Marine Corps Recruit Depot San Diego, California.  In March 2014, he reported for duty as the Sergeant Major for Education Command/Marine Corps University in Quantico, Virginia. 

In February 2016, he assumed his current duties as the Sergeant Major for Marine Corps Installations Pacific-Marine Corps Base Camp Butler, Japan.

Sergeant Major Siaw's personal awards include the Legion of Merit, the Bronze Star Medal, the Meritorious Service Medal (gold star in lieu of third award), the Navy and Marine Corps Commendation Medal (gold star in lieu of second award), the Navy and Marine Corps Achievement Medal (gold star in lieu of third award), and the Combat Action Ribbon (gold star in lieu of second award).