A military statement declaring them dead came days after rescuers recovered three bodies from the remote glacier where a huge avalanche buried them in early hours of April 7.
The military said that the decision to proclaim them "shuhada" (martyrs) was made after consultations with "religious leaders of prominence from all sects and factions".
The Army pledged it would "continue all out efforts to recover the bodies of all shuhada".
There had been an intense debate within the Army over the issue of how to describe the missing personnel after the avalanche hit the camp at Gyari on April 7.
Within days of the incident, experts and former Army officers had said it was unlikely that anyone in the camp had survived.
The Army, however, did not refer to the personnel as martyrs due to the sensitivities involved.
Search teams recovered the bodies of three soldiers on May 27, nearly 50 days after the avalanche.
"Nature and magnitude of the calamity is suggestive of no probability of recovering any person alive," the military statement said.
Noting that 52 days had passed since the avalanche, the statement further said: "Notwithstanding the resolve of troops employed on search operations, excavation work is taking time due to constraints imposed by terrain and weather."
The Army's decision to declare the 128 soldiers and 11 civilian employees buried under dozens of feet of snow as martyrs was also influenced by "socio-religious dimensions (and) implications, requirements to initiate the process of documentation, and reduction of the sufferings of the bereaved families", the statement said.
"From this deliberate exercise, it has been decided to declare the remaining brave soldiers as shuhada. This is being done with mixed feelings of pride, grief and above all unflinching resolve to continue all out efforts to recover the bodies of all shuhada," the statement said.
The avalanche has raised questions in Pakistan about the troop deployment in the hazardous terrain.
Indian and Pakistani troops have been engaged in a standoff on Siachen, described as the world’s highest and coldest battlefield, since 1984.
The guns have largely been silent since late 2003, when the two countries put in place a ceasefire along the frontiers in Jammu and Kashmir, and more troops have died on the glacier due to the adverse weather than combat.
The Defence Secretaries of India and Pakistan will hold their next round of talks on the military standoff on Siachen in Islamabad during June 11-12.