You can basically do two things, or a combination of these two:
- “Safe” option: Look for a good savings account to park your money. Interest rates up to 2 % at the time of writing. Note that the return is taxable.
Short guide to CHF fixed income options - Wiki - Mustachian Post Community - “Riskier” option: Invest your money in ETFs and take out a margin loan to pay your tax bills. Then pay back the margin loan when money comes in. At the time of writing, the margin rate for IBKR is 3%. The current rate can be found here: Margin Rates and Financing | Interactive Brokers U.K. Limited. Please note that the interest cost can be deducted from your income, so the after-tax rate might be 20-30 % lower.