Between January and June, 11,205 people filed asylum claims, mostly from Tunisia, Nigeria and Eritrea, the Swiss federal migration office said.
Over the past three decades, Swiss voters have regularly backed tougher asylum laws, most recently in a plebiscite in June that removed desertion from the military as grounds for receiving a safe haven.
The populist Swiss People's Party — the largest single force in parliament — has proven particularly skillful at leading the debate on the asylum issue.
It pushes a message that Switzerland is a magnet for bogus asylum-seekers who are really seeking a better life in the wealthy nation.
Critics on the left of the political spectrum reject that and say the country's rules efficiently filter out undeserving cases.
It can take years to process an asylum claim, and less than 12 percent of those whose cases were handled in 2012 were granted a haven.
The migration office said the 30.6 percent decrease in the number of asylum seekers in the first half of this year compared with the same period of 2012 was "unusual", notably because the rate of decline picked up pace with each passing month.
The spring months normally see a rise in numbers, the office said, adding that claims across Europe have risen by 10 percent over the same period.
But it is still too early to describe the fall in numbers in Switzerland as a trend, the office cautioned.
It also made no comment on whether Switzerland's change of stance on military deserters may have led asylum-seekers to turn elsewhere for fear of having their claims rejected.
Desertion has been the grounds for asylum most frequently cited by Eritreans, whose homeland imposes unlimited military service, with low wages, on all able-bodied men and women.
Some 48,000 people are currently in the process of seeking asylum in Switzerland, including the 28,631 who arrived in 2012, a 10-year record.
Last year's surge, attributed in part to the Arab Spring uprisings, took Switzerland back to a level last seen in the wake of the Balkan wars of the 1990s.