по итогам полугодия

[flos]

по итогам полугодия (падение продаж по итогам полугодия) - at the end of the half year???

[_03]

sales downturn/downfall based on semiannual/half-year results, imho

[SigGolfer]

I'm not 100% sure, but here are some options.

at the end of the second quarter (если финансовый год)

a mid-year decrease in sales

a decrease in sales, based on mid-year returns/totals

[flos]

какой у меня теперь выбор...

[SigGolfer]

I think that 'half-year' is British and 'mid-year' is more commonly used in the U.S., so it depends on your audience. I would avoid 'semiannual' - тут не подходит.

[10-4]

В формальном тексте можно:
Q1-2 results